Chemical and Mechanical Properties of Experimental Dental Composites as a Function of Formulation and Postcuring Thermal Treatment.

This study evaluated the influence of formulation and thermal treatment on the degree of conversion, fracture toughness, flexural strength, and elastic modulus of experimental composites. Six composites were analyzed at BisGMA : TEGDMA molar ratios of 1 : 1 and 7 : 3 with filler at 30, 50, and 70 wt%. The degree of conversion was analyzed by Fourier transform infrared spectroscopy, fracture toughness was measured using the single-edge notched beam, and flexural strength and elastic modulus were measured with the 3-point bend test. For all tests, one-half of the specimens received thermal treatment at 170°C for 10 min. Data were analyzed by the Kruskal-Wallis or ANOVA/Tukey's test (α = 5%). The 1 : 1 BisGMA : TEGDMA ratio showed higher properties than the 7 : 3 ratio. Although the material with 70% filler had a conversion lower than the one with 50%, it showed higher mechanical properties. The thermal treatment improved all properties in all materials. Therefore, the use of an equimolar ratio of BisGMA : TEGDMA can be paired with 70 wt% filler to design dental composites that possess increased advantageous physical and chemical properties. Furthermore, the simple and low-cost method of thermal treatment proposed for use in clinical dentistry has been shown to effectively improve the properties of all evaluated materials.

Does the casting mode influence microstructure, fracture and properties of different metal ceramic alloys?

The aim of the present study was to evaluate the tensile strength, elongation, microhardness, microstructure and fracture pattern of various metal ceramic alloys cast under different casting conditions. Two Ni-Cr alloys, Co-Cr and Pd-Ag were used. The casting conditions were as follows: electromagnetic induction under argon atmosphere, vacuum, using blowtorch without atmosphere control. For each condition, 16 specimens, each measuring 25 mm long and 2.5 mm in diameter, were obtained. Ultimate tensile strength (UTS) and elongation (EL) tests were performed using a Kratos machine. Vickers Microhardness (VM), fracture mode and microstructure were analyzed by SEM. UTS, EL and VM data were statistically analyzed using ANOVA. For UTS, alloy composition had a direct influence on casting condition of alloys (Wiron 99 and Remanium CD), with higher values shown when cast with Flame/Air (p < 0.05). The factors 'alloy" and 'casting condition" influenced the EL and VM results, generally presenting opposite results, i.e., alloy with high elongation value had lower hardness (Wiron 99), and casting condition with the lowest EL values had the highest VM values (blowtorch). Both factors had significant influence on the properties evaluated, and prosthetic laboratories should select the appropriate casting method for each alloy composition to obtain the desired property.

Does the casting mode influence microstructure, fracture and properties of different metal ceramic alloys?

The aim of the present study was to evaluate the tensile strength, elongation, microhardness, microstructure and fracture pattern of various metal ceramic alloys cast under different casting conditions. Two Ni-Cr alloys, Co-Cr and Pd-Ag were used. The casting conditions were as follows: electromagnetic induction under argon atmosphere, vacuum, using blowtorch without atmosphere control. For each condition, 16 specimens, each measuring 25 mm long and 2.5 mm in diameter, were obtained. Ultimate tensile strength (UTS) and elongation (EL) tests were performed using a Kratos machine. Vickers Microhardness (VM), fracture mode and microstructure were analyzed by SEM. UTS, EL and VM data were statistically analyzed using ANOVA. For UTS, alloy composition had a direct influence on casting condition of alloys (Wiron 99 and Remanium CD), with higher values shown when cast with Flame/Air (p < 0.05). The factors 'alloy" and 'casting condition" influenced the EL and VM results, generally presenting opposite results, i.e., alloy with high elongation value had lower hardness (Wiron 99), and casting condition with the lowest EL values had the highest VM values (blowtorch). Both factors had significant influence on the properties evaluated, and prosthetic laboratories should select the appropriate casting method for each alloy composition to obtain the desired property.

Heat treatment of a direct composite resin: influence on flexural strength.

The purpose of this study was to evaluate the flexural strength of a direct composite, for indirect application, that received heat treatment, with or without investment. One indirect composite was used for comparison. For determination of the heat treatment temperature, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were performed, considering the initial weight loss temperature and glass transition temperature (Tg). Then, after photoactivation (600 mW/cm(2) - 40 s), the specimens (10 x 2 x 2 mm) were heat-treated following these conditions: 170 masculineC for 5, 10 or 15 min, embedded or not embedded in investment. Flexural strength was assessed as a means to evaluate the influence of different heat treatment periods and investment embedding on mechanical properties. The data were analyzed by ANOVA and Tukey's test (alpha = 0.05). TGA showed an initial weight loss temperature of 180 masculineC and DSC showed a Tg value of 157 degrees C. Heat treatment was conducted in an oven (Flli Manfredi, Italy), after 37 degrees C storage for 48 h. Flexural strength was evaluated after 120 h at 37 degrees C storage. The results showed that different periods and investment embedding presented similar statistical values. Nevertheless, the direct composite resin with treatments presented higher values (178.7 MPa) compared to the indirect composite resin (146.0 MPa) and the same direct composite submitted to photoactivation only (151.7 MPa). Within the limitations of this study, it could be concluded that the heat treatment increased the flexural strength of the direct composite studied, leading to higher mechanical strength compared to the indirect composite.

Artificial methods of dentine caries induction: A hardness and morphological comparative study.

OBJECTIVE: To assess the ability of two chemical and a microbiological methods to produce dentine caries lesions resembling naturally developed dentine caries lesions. DESIGN: Forty sound second primary molars were divided into four experimental groups according to the method to produce artificial caries lesions: (1) sound (negative control); (2) acidified gel; (3) pH-cycling; and (4) microbiological, all for 14 days. Ten second primary molars presenting natural dentine caries lesions comprised the (5) positive control group. After the artificial caries induction, all samples were longitudinally sectioned and polished in order to obtain Knoop microhardness values from 10 to 500microm depth from the bottom of the cavities. Morphological analysis of the surfaces was carried out by SEM. Hardness data were compared among the five experimental groups using One-Way ANOVA and post hoc SNK's test. RESULTS: The hardness values of chemically created caries-like lesions did not differ from that of natural caries lesions on shallower depths. The results indicated that chemical caries induction methods promote a superficial demineralization and that pH-cycling is more effective than acidified gel. The former, produced a thicker layer of demineralization, with similar hardness values than natural lesions. Despite the microbiological method provided an excessive softness of the primary dentine, this method presented morphology more comparable to natural lesions. CONCLUSIONS: pH-cycling is more appropriated to simulate a substrate that resembles affected caries dentine layer, after caries removal. The microbiological method seems more indicated to simulate a dentine caries lesion with an infected layer, previously to caries removal.

Does adhesive thickness affect resin-dentin bond strength after thermal/load cycling?

This study evaluated the influence of adhesive layer thickness (ADL) on the resin-dentin bond strength of two adhesive systems (AS) after thermal and mechanical loading (TML). A flat superficial dentin surface was exposed with 600-grit SiC paper on 40 molars. After primer application, the adhesive layer of Scotchbond Multipurpose (SBMP) or Clearfil SE Bond (CSEB) was applied in one or two layers to a delimited area (52 mm2) and resin blocks (Filtek Z250) were built incrementally. Half of the sample was stored in distilled water (37 degrees C, 24 hours) and submitted to thermal (1,000; 5 degrees -55 degrees C) and mechanical cycles (500,000; 10kgf) [TML]. The other half was stored in distilled water (72 hours). The teeth were then sectioned to obtain sticks (0.8 mm2) to be tested under tensile mode (1.0 mm/minute). The fracture mode was analyzed at 400x. The BS from all sticks from the same tooth was averaged for statistical purposes. The data was analyzed by three-way ANOVA. The chi2 test was used (p < 0.05) to compare the frequency of pre-testing failure specimens. Higher BS values were observed for SBMP regardless of the ADL. The TML reduced the BS values irrespective of the adhesive employed and the ADL. A higher frequency of pre-testing failure specimens was observed for the cycled groups. A thicker adhesive layer, acting as an intermediate flexible layer, did not minimize the damage caused by thermal/mechanical load cycling for a three-step etch-and-rinse and two-step self-etch system.

Heat treatment of a direct composite resin: influence on flexural strength

The purpose of this study was to evaluate the flexural strength of a direct composite, for indirect application, that received heat treatment, with or without investment. One indirect composite was used for comparison. For determination of the heat treatment temperature, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were performed, considering the initial weight loss temperature and glass transition temperature (Tg). Then, after photoactivation (600 mW/cm©÷ - 40 s), the specimens (10 x 2 x 2 mm) were heat-treated following these conditions: 170¨¬C for 5, 10 or 15 min, embedded or not embedded in investment. Flexural strength was assessed as a means to evaluate the influence of different heat treatment periods and investment embedding on mechanical properties. The data were analyzed by ANOVA and Tukey's test (¥á = 0.05). TGA showed an initial weight loss temperature of 180¨¬C and DSC showed a Tg value of 157¡ÆC. Heat treatment was conducted in an oven (Flli Manfredi, Italy), after 37¡ÆC storage for 48 h. Flexural strength was evaluated after 120 h at 37¡ÆC storage. The results showed that different periods and investment embedding presented similar statistical values. Nevertheless, the direct composite resin with treatments presented higher values (178.7 MPa) compared to the indirect composite resin (146.0 MPa) and the same direct composite submitted to photoactivation only (151.7 MPa). Within the limitations of this study, it could be concluded that the heat treatment increased the flexural strength of the direct composite studied, leading to higher mechanical strength compared to the indirect composite.

Influência do volume de adesivo e das ciclagens térmica e mecânica na resistência de união resina-dentina em restaurações de alto fator de configuração cavitária / Influence of adhesive volume and thermal and mechanical loading in resin-dentin tensile bond strengths in restorations of high factor of cavity configuration

Interfaces adesivas flexíveis, com maior capacidade de dissipação de tensões poderiam prevenir falhas provenientes das tensões geradas durante a contração de polimerização, variações térmicas e esforços mastigatórios, sobretudo em restaurações com alto fator de configuração cavitária. Isso poderia ser obtido através do aumento da espessura da camada de adesivo. O objetivo deste trabalho é o de comparar a resistência de união (RU) à dentina do sistema adesivo Scotchbond multiuso aplicado com diferentes volumes de adesivo (uma ou duas camadas) e submetido ou não às ciclagens térmica e mecânica (CTM). As superfícies oclusal e radicular de 40 terceiros molares hígidos foram seccionadas perpendicularmente ao longo eixo dental por meio de disco diamantino. Os mesmos foram incluídos em anéis de PVC e posteriormente foram realizadas cavidades do tipo classe I (3 mm largura X 4 mm comprimento X 2 mm profundidade). O sistema adesivo foi aplicado através de uma micropipeta (4 ou 8J.11) e blocos de resina composta (Durafill) foram construídos em um único incremento. Metade da amostra foi armazenada em água destilada por 24h e submetida às ciclagens térmica (1.000; 5-55°C) e mecânica (500.000 ciclos /10 kgf). Já a outra metade foi armazenada em água destilada por 96h (período total do armazenamento e das ciclagens térmica e mecânica da outra metade da amostra). Após isso, os dentes foram seccionados, longitudinalmente, em cortes perpendiculares entre si, a fim de se obterem corpos-de-prova em formato tetragonal ("palito") com aproximadamente 0,8 mm2 de secção transversal, ficando a interface adesiva, entre a resina composta e a parede pulpar, perpendicular ao longo eixo do palito. Os palitos foram submetidos ao teste de microtração a 1,0 mm/min, os valores de RU, obtidos e o modo de fratura analisado. A RU foi expressa como um índice que incluiu os valores de RU dos diferentes padrões de fratura, além dos palitos prematuramente...

Dentin bonding interfaces with increased capacity of stress dissipation are able to prevent failures due to polymerization contraction, thermal and mechanical stresses. This would be obtained by increasing adhesive layer thickness. The purpose of this study was to compare the resin-dentin micro tensile bond strengths (BS) of Scotchbond Multipurpose adhesive system applied with different volumes of adhesive resin (one and two coats) submitted or not to thermal and mechanical loading (TML). A f/at superficial dentin surface was exposed on 40 third molars with a 600-grit SiC paper. Cavities (3 mm width X 4 mm length X 2 mm depth) were prepared with a high-speed handpiece under water. After conditioning and primer application, the adhesive layer was applied by a micropipette (4 or SIJI) and cavities restored (Ourafill) in one increment. Half of the sample was stored in distilled water for 24h and then submitted to thermal (1,000; 5-55°C) and mechanical cycles (500,000; 10kgf). The other half was stored in distilled water (96h). Teeth were then sectioned to obtain sticks (O.S mm2) from pulpal wall to be tested under tensile mode (1.0mm/min). The fracture mode was analyzed at 400X. BS was expressed as na index that included the BS values of different fracture patterns and the prematurely debonded specimens (O). The data was analyzed by three-way ANOVA. The x2 test was used (p<0.05) to compare the frequency of O specimens. Only main factor TML was significant (p

Reattachment of tooth fragment: an in vitro study.

Canine tooth fracture is common in dogs. Application of an esthetic and durable restoration may be challenging in veterinary dental practice. This study used traditional human dental laboratory methods to evaluate fracture strength of intact dog canine teeth and fractured teeth that had been restored by reattachment of the tooth fragment. The results showed that the teeth restored by reattachment of the tooth fragment supported a test load equal to 45.4 % of the load necessary to fracture intact canine teeth.

Chemical versus conventional caries removal techniques in primary teeth: a microhardness study.

The aim of this in vitro study was to assess the remaining dentinal surface after carious tooth tissue removal with a low speed conventional bur and two chemomechanical methods, (Papacárie and Carisolv), using the microhardness test. It was concluded that the hardness of the remaining dentin after carious tissue removal was lower than that obtained on healthy dentin, without significance between the different means of carious tissue removal (p<0.05).

Influence of aging treatments on microtensile bond strength of adhesive systems to primary dentin.

PURPOSE: The purpose of this study was to evaluate the in vitro influence of aging treatments on the microtensile bond strength of 2-step total-etch and self-etch adhesive systems to primary dentin. METHODS: Class I cavities (4 mm x 4 mm x 2 mm) were prepared in 80 extracted human primary molars divided into 8 groups (N=5) per adhesive system: (1) Single Bond (SI); and (2) Clearfil SE Bond (SE). Restored teeth were exposed to individual and combined aging treatments: (1) thermal (2,000 x at 5-55 degrees C; T); (2) mechanical load (100,000 x 80 N; M); (3) pH (mineralizing/demineralizing solutions; pH); and (4) control (24-hour water storage; C). Beam-shaped microtensile specimens were prepared (0.8 mm2 cross-sectional area) and loaded at a crosshead speed of 1.0 mm/minute in a universal testing machine. Fracture modes were examined by scanning electron microscope. RESULTS: Means (MPa) and standard deviations (+/-) were: (1) SI-T=24.17 (+/-1.99); (2) SI-M=25.64 (+/-9.75); (3) Si-pH=23.43 (+/-4.19); (4) SI-C=33.81 (+/-2.45); (5) SI-TM=18.60 (+/-3.57); (6) SI-TpH=23.90 (+/-4.28); (7) SI-MpH=20.96 (+/-4.06); (8) SI-TMpH=20.94 (+/-3.15); (9) SE-T=24.08 (+/-4.52); (10) SE-M=18.30 (+/-14.12); (11) SE-pH=19.22 (+/-8.93); (12) SE-C=37.80 (+/-7.28); (13) SE-TM=22.89 (+/-11.74); (14) SE-TpH=27.87 (+/-12.77); (15) SE-MpH=18.87 (+/-10.95); and (16) SE-TMpH=22.55 (+/-3.05). Both adhesive systems presented similar dentin bond strength (P>.05) which were significantly reduced when combined aging treatments were applied or when pH cycling (pH) was done. CONCLUSION(S): Combined aging treatments and also pH cycling alone influenced negatively adhesive bond strengths.

Inhibition of demineralization adjacent to tooth-colored restorations in primary teeth after 2 in vitro challenges.

PURPOSE: As clinical diagnosis of secondary caries is the most common reason for restoration replacement, fluoride-releasing restorative materials have been developed to address this problem. The purposes of this study were to verify demineralization inhibition produced by 5 restorative materials submitted to two methods of in vitro cariogenic challenge and verify whether these methods influence material behavior by means of polarized light microscopy and microhardness. METHODS: Class V cavities were prepared on buccal surfaces of 100 extracted primary molars and randomly restored with 1 of the 4 fluoride-releasing materials, Fuji IX, Vitremer, Dyract, Tetric Ceram, and Filtek Z250 as control material (N=10). Specimens were submitted to in vitro caries induction by two different methods, acid gel immersion, and pH cycling. Teeth submitted to gel were then sectioned and prepared for polarized light microscopy in water, while teeth cycled were prepared for microhardness evaluation. RESULTS: Polarized light microscopy: Means of demineralization areas (microm(2)) differed significantly, depending on the restorative material. Tukey's test revealed the smallest demineralization areas adjacent to Fuji IX and Vitremer restorations, with no difference between them (P>.05). The greatest demineralization area mean values were verified using Dyract and Filtek Z250, without differences between them (P>.05). Microhardness: Glass ionomer cements (GICs) performed better on the area of great cariogenic challenge, closer to the surface, than other materials indicating minor mineral loss during pH cycling. The compomer Dyract presented similar performance to GICs and composite resin Tetric Ceram, but it was better than Filtek Z250. CONCLUSION: The experimental model of caries lesion induction may influence material performance. GICs, however, are superior in preventing in vitro demineralization independently of the method.

Influence of adhesive systems on interfacial dentin gap formation in vitro.

PURPOSE: This study measured: 1) the interfacial dentin gap formation (IGW) of 2 etch & rinse and 3 self-etch systems with different degrees of acidity and determined the correlation between the smear layer thickness and interfacial gap formation after 1 day and 6 months water storage; 2) the hybrid layer thickness (HLT) produced by the adhesives applied under different smear layer thicknesses. METHODS AND MATERIALS: Three self-etch adhesives, a mild (Clearfil SE Bond; SE), a moderate (Optibond Solo Plus Self-Etch Primer; SO) and a strong (Tyrian Self Priming Etchant + One Step Plus; TY), and 2 etch & rinse systems (Single Bond; SB and Scotchbond Multi-Purpose Plus; SBMP) were studied. After flat grinding of the occlusal surfaces, 30 molars were sectioned longitudinally in 2 halves. Dentin surfaces with thick and thin smear layers were obtained for each tooth after polishing different sections on 60- and 600-grit SiC paper, respectively. A resin composite (Z250) build-up was made on each tooth section after randomized application of the adhesives. After 24-hour storage in water, resin-dentin bonded sticks (0.8 mm2) were prepared and divided for 1-day and 6-month measurements. The IGW was measured in a stereomicroscope under 400x. SEM micrographs were also made in order to measure the HLT provided by each adhesive. RESULTS: The thickness of the smear layer did not influence the mean gap width (p>0.05). The etch & rinse systems showed the lowest mean IGW in the 1-day group. Their IGW remained unchanged after 6 months. The self-etch systems showed wider initial IGW, which diminished after 6 months water storage, to sizes similar to the etch & rinse systems. The hybrid layer was thicker when bonded to #60 SiC-treated dentin; however, this difference was only statistically different for the 3-step etch & rinse system (p=0.001). The thickest hybrid layers were observed for the 2 etch & rinse adhesive systems and the thinnest for the mild self-etch. A negative and strong correlation between IGW and HLT was observed for the self-etching adhesive systems tested (r=80.2, p=0.01).

Effect of light-activation methods and water storage on the flexural strength of two composite resins and a compomer.

The present study evaluated the flexural strength of three composite resins recommended for direct esthetic restorations: a polyacid modified composite (Dyract AP), a unimodal composite resin (Filtek Z250) and a hybrid composite resin (Point 4). The variation factors, apart from the type of composite resin, were the light activation method and the water storage period. The composite resins were light-cured in continuous mode (40 s, 500 mW/cm2) or in ramp mode (0-800 mW/cm2 for 10 s followed by 30 s at 800 mW/cm2) and stored for 24 hours or 30 days in distilled water at 37 degrees C. The data were analyzed by ANOVA and Tukey test for multiple comparisons (alpha = 0.05). The composite resin Z250 presented the highest mean flexural strength (166.74 MPa) and Dyract AP presented the lowest one (129.76 MPa). The storage for 30 days decreased the flexural strength in ramp mode (24 h: 156.64 MPa; 30 days: 135.58 MPa). The light activation method alone did not lead to different flexural strength values.

Microhardness of Ni-Cr alloys under different casting conditions.

This study evaluated the microhardness of Ni-Cr alloys used in fixed prosthodontics after casting under different conditions. The casting conditions were: (1-flame/air torch) flame made of a gas/oxygen mixture and centrifugal casting machine in a non-controlled casting environment; (2-induction/argon) electromagnetic induction in an environment controlled with argon; (3-induction/vacuum) electromagnetic induction in a vacuum environment; (4-induction/air) electromagnetic induction in a non-controlled casting environment. The 3 alloys used were Ni-Cr-Mo-Ti, Ni-Cr-Mo-Be, and Ni-Cr-Mo-Nb. Four castings with 5 cylindrical, 15 mm-long specimens (diameter: 1.6 mm) in each casting ring were prepared. After casting, the specimens were embedded in resin and polished for Vickers microhardness (VH) measurements in a Shimadzu HMV-2 (1,000 g for 10 s). A total of 5 indentations were done for each ring, one in each specimen. The data was subjected to two-way ANOVA and Tukey's multiple comparison tests (alpha = 0.05). The VH values of Ni-Cr-Mo-Ti (422 +/- 7.8) were statistically higher (p < 0.05) than those of Ni-Cr-Mo-Nb (415 +/- 7.6). The lowest VH values were found for Ni-Cr-Mo-Be (359 +/- 10.7). The VH values obtained in the conditions induction/argon and induction/vacuum were similar (p > 0.05) and lower than the values obtained in the conditions induction/air and flame/air torch (p < 0.05). The VH values in the conditions induction/air and flame/air were similar (p > 0.05). The microhardness of the alloys is influenced by their composition and casting method. The hardness of the Ni-Cr alloys was higher when they were cast with the induction/air and flame/air torch methods.

Effect of light-activation methods and water storage on the flexural strength of two composite resins and a compomer

O presente estudo analisou a resistência à flexão de três compósitos recomendados para restaurações estéticas diretas: um compósito poliácido-modificado (Dyract AP), uma resina composta unimodal (Filtek Z250) e uma resina composta híbrida (Point 4). Os fatores de variação, além do tipo de compósito, foram o método de fotoativação e o período de armazenagem em água. Os materiais foram fotoativados continuamente por 40 s (500 mW/cm²) ou com intensidade de luz crescente (0-800 mW/cm² por 10 s seguidos de 30 s a 800 mW/cm²). Os períodos de armazenagem foram de 24 horas ou 30 dias em água destilada a 37°C. Os dados foram submetidos à análise de variância e ao teste de Tukey para comparações múltiplas (a = 0,05). A resina composta Z250 apresentou a maior média de resistência à flexão (166,74 MPa) e a Dyract AP, a menor (129,76 MPa). A armazenagem por 30 dias diminuiu a resistência à flexão para o método de fotoativação crescente (24 h: 156,64 MPa; 30 dias: 135,58 MPa). O método de fotoativação isoladamente não conduziu a diferentes valores de resistência à flexão.

Resistência de união à dentina com sistemas adesivos de fabricantes nacionais e internacionais / Dentin ond strength using national and international adhesive systems

Para este estudo, seccionaram-se 20 molares permanentes hígidos, no sentido do longo eixo, a fim de obter 40 espécimes, que foram divididos em quatro grupos experimentais (n=10): Single Bond (SB), Clearfil SE Bond (SE), Magic Bond DE (MB) e Self-Etch Bond (SEB). Os sistemas adesivos foram aplicados, seguindo-se as recomendações dos fabricantes, sobre superfície dentinária plana, previamente preparada, e blocos de compósito foram construídos. Após 24 horas, os espécimes foram preparados para o teste de microtração (área de secção aproximada de 0,8mm2). Os valores médios obtidos (MPa) foram submetidos à análise de variância. Os resultados mostram que a resistência de união dos sistemas adesivos nacionais (MB e SEB) é inferior à dos outros sistemas (SB e SE).

Resistência à tração e alongamento de ligas de Ni-Cr fundidas sob diferentes condições / Tensile strength and elongation of Ni-Cr alloys under different casting conditions

Este trabalho avaliou a resistência à tração e alongamento de ligas a base de Ni-Cr fundidas sob diferentes condições (CF). Foram utilizadas três ligas: Ni-Cr-Mo-Ti, Ni-Cr-Mo-Be e Ni-Cr-Mo-Nb, fundidas em 4 CF: indução/argônio (IA), indução/vácuo (IV), indução/controle (IATM) e maçarico (gás/O2). As composições das ligas foram analisadas por meio de um espectrômetro de florescência de raios X. Foram preparados 4 anéis de fundição, sendo que cada anel apresentava 5 espécimes na forma de cilindros (45m x 1,6m). O teste de resistência à tração (RT) e alongamento (AL) foi conduzido em uma máquina Riehle (0,5 mm/min). Os dados de RT e AL foram avaliados pela análise de variância e teste de Tukey (a=0,05) para contraste de média. Quanto à RT, somente os fatores principais (liga e condições de fundições) foram significantes (p<0,05). A liga Ni-Cr-Mo-Ti teve a maior média (1.012 ± 59 MPa), seguida da liga Ni-Cr-Mo-Be (870 ± 86 MPa) e da liga de Ni-Cr-Mo-Nb (629 ± 84 MPa), todas diferentes entre si (p<0,05). Já para as condições de fundição, apenas o maçarico (889 ± 188 MPa) teve valores significantemente maiores do que as outras condições (p<0,05). As condições IV (818 ± 184 MPa), IATM (817 ± 198 MPa) e IA (800 ± 165 MPa)obtiveram valores semelhantes entre si (p>0,05). Para o AL, apenas o fator principal liga apresentou diferenças (p<0,05). A liga Ni-Cr-Mo-Be (1,63 ± 0,4) apresentou o maior valor; Ni-Cr-Mo-Nb, o menor (0,51 ± 0,1) e a Ni-Cr-Mo-Ti, valores intermediários (1,19 ± 0,3), sendo todas diferentes entre si (p<0,05). Tanto a composição quanto as condições de fundição influíram na resistência à tração, mas apenas as ligas influenciaram o alongamento.

Microhardness of Ni-Cr alloys under different casting conditions

Este estudo avaliou a microdureza de ligas de Ni-Cr usadas em prótese fixa fundidas sob diferentes condições. As condições de fundição foram: (1-maçarico) chama composta por uma mistura de gás/oxigênio e centrífuga sem o controle do ambiente de fundição; (2-indução/argônio) indução eletromagnética com o ambiente controlado com argônio; (3-indução/vácuo) indução eletromagnética com o ambiente sob vácuo; (4-indução/ar) indução eletromagnética sem o controle da atmosfera. Foram utilizadas três ligas: Ni-Cr-Mo-Ti, Ni-Cr-Mo-Be e Ni-Cr-Mo-Nb. Foram realizadas 4 fundições com 5 espécimes cilíndricos de 15 mm de comprimento (diâmetro de 1,6 mm). Depois das fundições os espécimes foram embutidos e polidos para as mensurações de microdureza Vickers (VH) em um Shimadzu HMV-2 (1.000 g por 10 s). Um total de 5 indentações foram feitas por anel, uma em cada espécime. Os dados de VH foram avaliados pelos testes de ANOVA e Tukey (a = 0,05) para contraste de média. A microdureza das ligas apresentou a seguinte ordem: Ni-Cr-Mo-Ti (422 ± 7,8) > Ni-Cr-Mo-Nb (415 ± 7,6) > Ni-Cr-Mo-Be (359 ± 10,7), sendo diferentes entre si. Os valores obtidos nas condições indução/argônio e indução/vácuo foram semelhantes entre si (p > 0,05) e menores que os obtidos nas condições indução/ar e maçarico, estes últimos semelhantes entre si (p > 0,05). A microdureza das ligas é dependente da composição da liga e do método de fundição. A dureza das ligas de Ni-Cr foi maior quando fundidas nas condições indução/ar e maçarico.

O mercúrio no consultório dentário – minimizando os riscos / Mercury in the dental office – risk reduction

Apresentamos um resumo dos perigos que comporta o uso do mercúrio em consultórios dentários e o protocolo de uso que visa minimizar os riscos inerentes ao uso de amálgama e à manipulação dos resíduos gerados por ele. O amálgama é um material seguro para o paciente, para a equipe odontológica e para o ambiente desde que sejam tomados os cuidados assinalados neste protocolo